A limestone and fieldstone structure that houses the namesake bell of Bell Tower Park commemorates soldiers from the Riverdale, Spuyten Duyvil, and Kingsborough neighborhoods of the Bronx who fought in WWI. The bell dates back to 1762 when it was cast for a Mexican monastery. It was later captured by General Winfield Scott during the Mexican War and brought back to NYC, where it was first housed at a fire look-out at Jefferson Market in Greenwich Village and later moved to a firehouse in Riverdale before ending up in its current location.

It's not an official monument of the city, but a fraction of the Berlin Wall stands inside the lobby of 520 Madison Avenue. Jerry Speyer, the chairman of Tishman Speyer, purchased the segment of the wall for about $50,000 in 1990. The segment formerly stood in a pocket park behind 520 Madison, but has since been restored and moved into the lobby, per a New York Times article.

This unassuming sculpture in Christopher Park pays tribute to the gay rights movement and the events that unfolded at the Stonewall Inn, a seminal meeting spot in the movement that's adjacent to the park. The sculpture was created by George Segal who stipulated in the terms of his commission that his design for the sculpture must "show the affection that is the hallmark of gay people ...and it had to have equal representation of men and women."

Some may recognize it as the entrance to the South Street Seaport, but this little white lighthouse is actually a memorial commemorating the Titanic. It was erected at the behest of Molly Brown, a Titanic survivor who garnered the nickname The Unsinkable..., in the year following the tragedy. The memorial was repositioned from the roof of the Seamen's Church Institute in 1967 to its current location.

One of the many monuments in The Battery, the American Merchant Marines Memorial commemorates all lives lost at sea. Scouting NY says the memorial was designed off of a photograph taken during WWII by Nazis after their U-boat attacked an American merchant marine vessel.

On June 15, 1904, a passenger paddle boat named the PS Slocum set off into the East River carrying over 1,300 passengers and crew members. Soon after the boat cast off, a fire spread on board. A majority of the passengers, women and children who were part of the German-American community of the Lower East Side, didn't know how to swim. That spelled certain disaster. Over 1,000 people died in the incident, the largest death toll in a single domestic event until September 11.

Alexander Skene is not a household name, but his work has reformed the practice of modern-day gynecology. A Scot who took up residence in Brooklyn when it was still its own city, Skene was the president of Long Island College Hospital from 1893 through 1899, and was a founder of the American Gynecological Society. He is considered one of the foremost thinkers in the field in the late 1800s.

The September 11 Memorial on Staten Island was built in 2004 and remembers the 275 borough residents who were killed in the September 11 attacks and 1993 World Trade Center bombing. The design is the work of New York architect Masayuki Sono and is called Postcards after the two 30-foot pillars that are lined with plaques bearing the name and birthdate of those who perished in the attacks, including the place of work of those who died on September 11. The two structures frame the space on the skyline where the original World Trade Center towers once stood.